Neural activity in the brain can be influenced by electrical energy that is supplied from a waveform generator or other type of device. Various patient perceptions and/or neural functions can thus be promoted or disrupted by applying an electrical or magnetic signal to the brain. As a result, researchers have attempted to treat various neurological conditions using electrical or magnetic stimulation signals to control or affect brain functions. For example, Deep Brain Stimulation (DBS) has shown promising results for reducing some of the symptoms associated with Parkinson's Disease, which results in movement or muscle control problems and is debilitating to a great number of individuals worldwide.
Neural activity is governed by electrical impulses or “action potentials” generated in and propagated by neurons. While in a quiescent state, a neuron is negatively polarized, and exhibits a resting membrane potential that is typically between −70 and −60 mV. Through electrical or chemical connections known as synapses, any given neuron receives from other neurons excitatory and inhibitory input signals or stimuli. A neuron integrates the excitatory and inhibitory input signals it receives, and generates or fires a series of action potentials in the event that the integration exceeds a threshold potential. A neural firing threshold may be, for example, approximately −55 mV. Action potentials propagate to the neuron's synapses, where they are conveyed to other neurons to which the neuron is synaptically connected.
A neural stimulation system may comprise a pulse generator and an electrode assembly. One or more portions of a neural stimulation system may be implanted in a patient's body. For example, an implanted pulse generator may commonly be encased in a hermetically sealed housing and surgically implanted in a subclavicular location. An electrode assembly may be implanted to deliver stimulation signals to a stimulation site, and is electrically coupled to the pulse generator via biocompatibly sealed lead wires. A power source is contained within the housing of the pulse generator and is generally a battery.
Neural stimulation is generally delivered or applied to a patient in accordance with a treatment protocol. Typically, a treatment protocol specifies an optimal or best set of neural stimulation parameters directed toward maximally alleviating one or more patient symptoms through neural stimulation applied in a continuous, generally continuous, or nearly continuous manner. Unfortunately, under a conventional treatment protocol, neural stimulation efficacy may wane or degrade over time.
Since a battery has a finite charge storage capacity, a battery will expire or become depleted, thereby interrupting the patient's treatment. Various types of neural stimulation systems may include a nonrechargable battery that may last approximately two to three years. After an implanted battery is exhausted, another surgery is typically required to replace the pulse generator. As with any surgery, complications may arise, and subsequent incisions to the implanted site may prove troublesome due to scar tissue, implantation site sensitivities, and/or other conditions.